This invention relates to measurement for .gamma.-ray dose rate. The .gamma.-ray dose rate counters commonly used in the atomic energy facilities are generally operating at low dose rate, but in abnormal conditions they are operating at extremely high dose rate. Therefore, it is desirable that all the dose rate meters can operate to measure the dose rate without substantial error in the indication even at the high dose rate. This invention particularly relates to a detector in which the dose rate can be measured over a quite wide range of dose rate by only one detector within allowable error limit from a low dose rate to a high dose rate which may reach beyond a practically anticipated value.
In the system for measuring dose rate of the prior art, in the region of low dose rate Geiger-Muller (GM) counting tubes or scintillation detectors having linearity in that region are utilized while in the region of high dose rate ionization chamber detectors having linearity in that region are utilized. Therefore, it has been necessary to change the kind of GM counting tube having different .gamma.-ray efficiency according to the dose rate or to change the kind of scintillator having different scintillation efficiency from large size to small size as the dose rate increases, in order to measure a wide range of dose rate using only one kind of device.
The prior system explained above is not only economically quite advantageous but also extremely complicated in operation itself.